The present invention relates to pressure vessels for storing highly pressurized fluid material, and particularly to portable, lightweight pressure vessels of the type wherein a thin, lightweight metallic liner having a cylindrical portion and a pair of dome-shaped end portions is completely overwrapped by a plurality of layers of filament material. The invention is particularly applicable to liners wrapped with resin-coated, single-glass filaments (commonly called wet-windings or pre-impregnated windings). The present invention further relates to an overwrapping technique wherein the filament wrapping sequence is specifically designed to reinforce the junction of the cylindrical portion with each of the dome portions.
The term "completely overwrapped", as used herein and in the art, encompasses a vessel in which the cylindrical portion and the dome-shaped end portions are completely overwrapped, but which also may include small neck-shaped portions at the outer extremities of the dome-shaped portions which may, or may not, be overwrapped. This will be readily apparent to those skilled in the art.
A pressure vessel made in accordance with the present invention may be particularly designed for use in a compressed air breathing system of the type which would be carried by a fireman or scuba diver. Pressure vessels of this type must, of course, be designed with a view toward obtaining minimum weight-maximum volume characteristics, while nonetheless being capable of satisfying the safety objectives of federal and local regulatory agencies. For example, a pressure vessel made in accordance with the present invention has been specifically designed to satisfy the following specifications:
1. Maximum weight of 9.0 pounds,
2. Maximum operating pressure of 4500 PSIG (charge pressure of 4,000 PSIG),
3. Minimum contained volume of 280 cubic inches,
4. Proof pressure 6750 PSIG,
5. Minimum burst pressure of 9,000 PSIG,
6. Inexpensive enough to justify commercial production.
It should be noted that the foregoing specifications are set forth basically as an example of the characteristics which a pressure vessel manufactured in accordance with the present invention can satisfy. More particularly, the foregoing specifications indicate the high operating pressures (i.e. 4500 PSIG for example) at which a pressure vessel in accordance with the present invention can function and yet be relatively light in weight and inexpensive enough to satisfy commercial production cost requirements.
It is contemplated that pressure vessels for many and varied applications may be manufactured in accordance with the present invention. Further examples of pressure vessels which can be made in accordance with the present invention include skin diving breathing apparatus, and storage bottles for cryogens, chemicals, fuels and gases. In fact, the method of manufacture in accordance with the present invention may be utilized to produce any overwrapped vessel where both polar and cylindrical reinforcement is utilized. Naturally, the specifications and operating characteristics may vary for pressure vessels for uses other than those set forth in the specific example set forth above.
Known pressure vessels which can operate at high pressures include all metallic vessels. An all metallic vessel which would satisfy the strength requirements for operating at high pressures generally requires a grade of steel whose cost makes commercial production of such a vessel unfeasible.
Pressure vessels which are known and which are less expensive to produce are those where a liner is overwrapped with a plurality of filament layers. Typical of the overwrapping technique for such a vessel is a 2-step overwrapping technique wherein a liner is completely overwrapped in the polar direction, followed by a plurality of circular windings about the cylindrical portion. Particularly when overwrapping is performed by wet winding, and the 2-step wrapping sequence is used, the vessel is generally inadequately reinforced at what applicant has found to be the most critical area of the vessel, i.e., the junction of the cylindrical region with the dome region. This is because filament material cannot be effectively wound cylindrically over the junction or it would tend to slough or slip down the dome area.